Scrollbars on JTextArea in a JScrollPane do not work

I'm having trouble getting a JTextArea to scroll. I'm not sure how you can mess up a JScrollPane but I seem to have and I just can't see it. It's all part of a larger project but the code below is how I'm creating a JTextArea and adding it to a JScrollPane. When you type beyond the edge of the text area the scrollbar doesn't appear. Setting the vertical scrollbar to always on gives a scrollbar that doesn't do anything.

import javax.swing.*;
import java.awt.*;

public class TextAreaT开发者_运维百科est extends JFrame{

    public TextAreaTest() {
     super("Text Area Scroller");

     Container c = getContentPane();

     JTextArea textarea = new JTextArea();
     textarea.setPreferredSize(new Dimension(300, 50));
     textarea.setLineWrap(true);
     textarea.setText("xx\nxx\nxx\nxx\nxx\nxx\nxx\nxx\nxx\nxx\nxx\nxx\nxx\nxx\n");

     JScrollPane scroller = new JScrollPane(textarea);

     c.add(scroller, BorderLayout.CENTER);
     pack();
     setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public static void main(String args[]){
     TextAreaTest instance = new TextAreaTest();
     instance.setVisible(true);
    }
}

I've tried setting the text area text, or rows and columns, in the constructor, neither of which worked. It's doing my head in. Any ideas?

Set the preferred size of the scroll pane rather than the text area.

The others are right about the size. As an aside, consider starting on the Event Dispatch Thread (EDT):

public static void main(String args[]) {
    EventQueue.invokeLater(new Runnable() {

        @Override
        public void run() {
            new TextAreaTest().setVisible(true);
        }
    });
}

Use this code

import javax.swing.*;
public class ScrollingTextArea 
{
JFrame f;
JTextArea ta;
JScrollPane scrolltxt;

public ScrollingTextArea() 
{
    // TODO Auto-generated constructor stub

    f=new JFrame();
    f.setLayout(null);
    f.setVisible(true);
    f.setSize(500,500);
    ta=new JTextArea();
    ta.setBounds(5,5,100,200);

    scrolltxt=new JScrollPane(ta);
    scrolltxt.setBounds(3,3,400,400);

    f.add(scrolltxt);

}

public static void main(String[] args)
{
    new ScrollingTextArea();
}

}